sql can't figure out the query - mysql

Question

I have three tables:
CREATE TABLE IF NOT EXISTS `contacts` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`providerId` int(10) unsigned NOT NULL DEFAULT '0',
`requestId` int(10) unsigned NOT NULL DEFAULT '0',
`status` binary(1) NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
)
CREATE TABLE IF NOT EXISTS `messages` (
`id` int(255) NOT NULL AUTO_INCREMENT,
`fromuid` int(255) NOT NULL,
`touid` int(255) NOT NULL,
`sentdt` datetime NOT NULL,
`read` tinyint(1) NOT NULL DEFAULT '0',
`readdt` datetime DEFAULT NULL,
`messagetext` longtext CHARACTER SET utf8 COLLATE utf8_bin NOT NULL,
PRIMARY KEY (`id`),
KEY `id` (`id`)
)
CREATE TABLE IF NOT EXISTS `users` (
`id` bigint(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
`email` varchar(255) DEFAULT NULL,
`mobile` varchar(15) NOT NULL,
`password` varchar(255) NOT NULL,
`city` varchar(255) NOT NULL,
`zip` varchar(15) DEFAULT NULL,
`device` varchar(50) DEFAULT NULL,
`version` varchar(10) DEFAULT NULL,
`photo` varchar(255) DEFAULT NULL,
`created` datetime NOT NULL,
`live` enum('0','1') NOT NULL DEFAULT '1',
`authenticationTime` datetime NOT NULL,
`userKey` varchar(255) DEFAULT NULL,
`IP` varchar(50) DEFAULT NULL,
`port` int(10) DEFAULT '0',
PRIMARY KEY (`id`),
KEY `firstname` (`mobile`,`city`,`zip`)
)
And this SQL query that finds out friends/contacts for specified user (user id 1 in this case):
SELECT u.id
,u.mobile
,u.name
,(NOW() - u.authenticationTime) AS authenticateTimeDifference
,u.IP
,f.providerid
,f.requestid
,f.status
,u.port
FROM contacts f
LEFT JOIN users u ON u.id =
IF (
f.providerid = 1
,f.requestid
,f.providerid
) WHERE (
f.providerid = 1
AND f.status = 1
)
OR f.requestid = 1
That works fine but I want to be able to also join messages table and show user's friends/contacts who have talked latest (meaning latest conversations first) with order by messages.sentdt desc option but I am unable to figure out how to do that, I tried all joins but none worked :(
Your help will be greatly appreciated. Thanks
Update
Here is sample data above query returns:
In that same resultset, I want to be able to sort based on order by messages.sentdt desc but I am not sure how to pull that in and sort resultset by latest message first

Answer 1

Try this:
select u.id
, u.mobile
, u.name
, (NOW() - u.authenticationTime) as authenticateTimeDifference
, u.IP
, f.providerid
, f.requestid
, f.status
, u.port
from contacts f
left join users u
on u.id = if (f.providerid = 1, f.requestid, f.providerid)
left join (select fromuid, max(sentdt) as sentdt from messages group by fromuid) m
on m.fromuid = if (f.providerid = 1, f.providerid, f.requestid)
where (f.providerid = 1 and f.status = 1)
or f.requestid = 1
order by m.sentdt